High-frequency signaling system



Oct. 29, 19219. Ev. ROBINSON 1 733,824

HI GH FREQUENCY SIGNALING SYSTEM Filed Aug. 20, 1923. 3 Sheets-Sheet l //2 writer B M Attorney Oct. 29, 1929.

E. Y. ROBINSON I 1,733,824

HIGH FREQUENCY SIGNALING SYSTEM Filed Aug. 20, 1925 3 Sheets-Sheet 2 hare/7207."

Oct. 29, 1929. ROBINSON 1,733,824

HIGH FREQUENCY SIGNALING SYSTEM Filed Aug. 20, 1925 3 Sheets-Sheet 3 Patented a. 29, .1929

PATENT OFFICE ERNEST YEdMAN ROBINSON, OF MANCHESTER, ENGLAND HIGH-'FREQNENCY SIGNALING SYSTEM Application filed August 20, 1923, Serial No. 658,408, and in Great Britain August 22, 1922.

This invention relates to improvements in changes of decrement. Moreover, it may be methods of reception in high frequency signaling systems.

In high frequency signaling systems, such as wireless telegraphy and telephony, it IS 1 5 well known that reducing the resistance of the antenna or oscillatory circuits connected thereto as by connecting a negative resistance device, for example regenerative threeelectrode valves thereto, results in an increase 0 of signal strength and increased selectivity.

Apart from the question of the stability of the circuits howeverthere is a limit to the degree of signal strength which may be obtained in this manner owing to the time lag which occurs in building up and dissipating the oscillations which are induced in the antenna or antenna circuits. Thus, in the case of sparktelegraphy, no gain in signal strength occurs if the resistance of the antenna is reduced to such a low degree that the oscillations from one spark train merge into the next; in the case of continuous wave telegraphy if the resistance of the antenna is reduced to too low a value one signal will not be clear of the receiving apparatus before the next arrives; in the case of telephony it is necessary in order to produce distortionless reception that none of the oscillatory circuits in the receiving apparatus should have a lower decrement than the highest decrement in the received waves. Moreover, in high speed telegraphy even when the decrement of the receiving circuit is relatively high the speed of sending is limited by the said circuits because even if the decrement is high enough togensure rapid dying away of the signal oscillations the growth of the oscillations is limited by the energy capacity of the antenna and circuits connected thereto.

In accordance with this invention it is arranged that the decrement of the antenna or the oscillatory circuits employed or both is decreased when the signal is increasing in strength and is increased when the signal is decreasing in strength and preferably remains substantially constant when the signal strength is zero or is constant. Furthermore, in the preferred method it is arranged that the incoming signal itself effects these arranged that at some times when the signal is increasing in strength the decrement of the circuit or circuits is made negative so that a relatively large amount of power is locally supplied .in order effectively to compensate for the energy capacity of the antenna and ,oscillatory circuits connected'thereto. Preferably it is arranged that the change of decrement of the antenna is proportional to the rate of change .of signal strength; it is of course of such a sign that the above effects occur.

As a result of this invention it is possible to employ receiving circuits having much lower decrements than has hitherto been possible and thus the receiver maybe made highly sensitive and selective without producing such effects as distortion or the merging of one signal into the next. Another result of this invention is that when it is employed with a plurality of receiving circuits atmospherics are reduced as will behereinafter described. To enable the invention to be clearly understood it will now be described with reference to the accompanying drawings in which Fig. 1 is an elementary circuit diagram illustrating themethod of reception according to the invention; Figs. 2"and-3 are characteristic curves of a three-electrode Valve;

'Figs. 4, 5 and 6 are electrical diagrams of three forms of reception circuits in accordance with the invention; Fig.7 is an electrical diagram of a reception circuit in accordance wlth the lnvention for receiving signals transmitted on two wave lengths, and

Fig. 8 is acharacteristic curve of a typical negatiye resistance device.

In Fig. l'of the drawings, 1 represents an antenna connected to a loading coil 2, across which is connected a circuit containing a de tector 8. Included in the antenna circuit is a device 4 the resistance of which-may be controlled and which preferably also serves to introduce suiiiciently negative resistance in the antenna circuit to reduce the constant component of the antenna resistance to a low value. The rectified currents pass through the primary winding 5 of a trans 5 ing 6 thereof is proportional to the. rate ofchange of amplitude of the antenna oscillations and this secondary electromotive force is caused to control the value of the resistance ofthe device 4,. The signal may be caused 6' to operate telephones or relays (not shown) a through the medium, for example, of a transformer 7 connected in the detector circuit as indicated by'dotted lines.

The decrement of the circuits may be varied by varying the output of a negative re-' sistance device and examples of this method willbe hereinafter described but in the'preferred method it is arranged that a vacuum electric device, forexample a three-electrode valve is coupled to the circuit so that it introduces resistanceintothe circuit and the resistance isvaried by means of the'vacuum electric device while" the resistance of the whole circuit is reduced to a low value by 5 means of a negative resistance device, forex- .ample' a regenerative three-electrode valve.

Alternatively these two effects may be produce'dby means of one reactively coupled valve and the variable resistance produced so by means of the grid current flowing therein? Referring to Figs. 2 and 3'which illustrate respectively theanode current-grid voltage characteristic of a three-electrode valve and the differential conductance of the valve, it

will be seen that when the grid voltage Eg .is such that the representative point is on the lower curved portion ofthe. anode characteristic the differential conductance A of the valve is represented by the rising portion '40 8 .of the curve shown in Fig. 3. If the curved- I portion of'the anode characteristic follows a square lawthen the corresponding portion of the differential conductance curve follows a= straight'line law. Therefore 1n the preferred method a valve is coupled tothe antenna and is employed as a variable resistance the resistanceof thevalve'fbeing' varied varying the rid potential thereof, whilst the resistance 0 the circuit is reduced to a low valueby means of a negative resistance device such for example as a dynatron or-a reactively coupled three-electrode valve.

Fig. 4 lllustrates this method, Q Theantenna 'is shown at 9-and the antennaloading coil at 10. The variable resistance valve is shown at 11;'it has an anode battery at 12 and is coupled to the'antenna by means of an inductance 13}. The receivedoscillations are amplified if necessary by a valve'19 and are detected by the valve 14. The rectified current passes through the rimaryof the. trans-- former 15 which preferahly comprises a small number of turns well spaced so that the shunted capacit is small, the transformer b6; ing so designed that the electromotive force induced across the secondary thereof is proportional to the rate of change of current flowing through the primary. That is to say, the transformer windings are preferably arranged so that the distributed capacity across each windin and from one Winding to 'another is ma e small. This may-beefiected.

by building the windings in sections-well spaced from each other and from the iron core preferably so that the major portion of 7 the dielectric is air and the sections ofthe two windings interlink with each other. Furthermore, it is preferable in order that the distributed capacity shall be low that the transformation ratio is unity and that a relatively large air gap is provided in the iron circuit. It is further desirable that the average inputreaction of this transformer is considerably less than the differential anode resistance of the valvein order that the current flowing therein is proportional to the mean value of the electromotive force applied to the grid of the said valve. The primary ofthe trans-' former should be shunted by a small condenser (not shown) in order to. pass the high frequency component of the rectified current The capacity of this condenser shoiild be so lowthat the oscillatory-circuit so formed is not in resonance to any of the high frequency components present in the rectified current. The secondary of the transformer 15 is cou-- pled by the conductors 15 to the grid of-the valve 11. A suitable grid biasing battery 16 is employed and the mean grid potential is adjusted so that the representative point is on' the curved portion ;of the characteristic. Preferably this grid biasing electromotive force is negative so that the load on the trans-' former is negligible. The resistance of the antenna circuit is reduced to a low value by means of the back coupling provided the. coil 17 WVhen the signal strength is zero or constant, the electromotive force induced in the transformer 15 is zero and the grid potential of valve 11 is due to that of the grid biasing battery.- Suppose it is representedby the point 18 on the curves of Figs. 2. and 3.- Dur-- ing an increase ofsignal strength the grid 0- tential of the valve 11 becomes more negatlve and the representative point 18 'moves down I the curve so that the resultantresistance of the antenna is decreased and it'may even become negative, that is, the oscillations ma be generated locally. As a result the owth of oscillations is facilitated. When t e signal decreases in strength'the representative point .18 travels up the curve and the existing oscil- I I lations are value. 1

,Imorder that the circuitfshould operate withoubftback-lash. as is requisite if the antenna resistance becomes at any time negative, 4 the mean grid potential of the valve 19 should be such that the-representative point is on) the straight portion of the "characteristic or quickly reduced to-their proper when there is no straight portion, the point of-infle'xion. It should however be noted that if the mean grid potential of this valveis positive so that a grid current flows, the grid voltages will not necessarily be at the point of infiexion but may be displaced therefrom. The amount of displacement will depend upon the curvature of the grid current characteristic of the valve. The signals may be applied to telephones, recorders or the like by means for example of the transformer 20.

In Fig. 5 which illustrates connections which may be employed when it is desired to receive the incoming signal by the heterodyne method, the decrement of the antenna is varied in the manner described with reference to Fig. 4, the same elements being designated by %he same reference characters in these two led off through an amplifier 21 to a separate detector 21 and are detected by the heterodyne method by inducing oscillations of suitable frequency in the grid circuit of this detector by means of the local generator 22 I which may, consist for example of a valve oscillation generator.

. In-Fig. 6 which illustrates a. method wherein the decrement of the aerial may be varied by means of the grid current flowing in the first valve 19 connected therewith,the grid biasproduced by the grid biasing battery 16 is such that the mean grid potential is.

positive and the means grid potential is varied in proportion to the rat of change of the incoming signal so that owing to the curvature of the grid current characteristic the decrement of the aerial, which in thisexample is shown as a frame aerial 9, is varied in accordance with the rate of change of the incoming signal. The transformer producing the electromotive force necessary to produce these changes of decrement is indicated at 23 and is coupled to the grid circuit through the conductors 23 one of" which is connected to one terminal'of theaerial 9 which has a tuning conductor 9" connected across its terminals, the other terminal of said aerial being connected to the grid of the valve 19, so thatthe fluctuations'in' the electromotive force produced by the transformer 23 will be impressed onthe grid of the valve 19. In order that the circuit should operate without back-lash inca'se oscillations are either intentionally or accidentally produced in the aeria-L'it is necessary that the characteristic of the valve should have a long straight portion so that the negative resistance effect introduced by means of the back coupling from the valves through the back coupling coils 17 is constant although the mean grid potential may change within Q wide limits in order toproduce the necessary res, whilst the incoming oscillations are may be connected to a telephone or the as in Figs. 4 and 5. v

In the examples illustrated the output current of the receiving device has been passed through the primary of a transformer and When transmission is effected on more like,

than one wave length, for example when a spacing Wave is employed, then a plurality of receiving devices each. resonant to one of.

the wave lengths employed may be used, the output circuits of the'said receiving circuits being interconnected to the devices producing variable decrement so that the variations of signal current in one receiving device control the decrement of circuit or circuits of another receiving device.

Fig. 7 illustrates an application of this modification of the invention to the reception of continuous wave telegraphy wherein a spacing wave is transmitted. Two antennae are employed for the reception of the signal. The antenna 24 is tuned to the signal wave and the antenna 25 to the spacing wave bythe tuning condensers 24 and 25 respective- 1y connected across their terminals. A The oscillations induced in the antenna 24 are amplified by means of the high frequency amplifier 26 and may bedetected by the heterod'yne methodv as in Fig. 5, and the oscillations are also detected in a detector 27. The output circuit of this detector 27 consists of the transformer 28 which is so designed that the voltage induced across its secondary circuit is proportional to the rate of" change of current in the primary. The

secondary of the transformer 2 8 i s connected by the conductors 28 to the grid of a valve 29 which is placed across' the aerial 25 by the conductors 29 and 29 so that it produces a variable decrement therein. said decrement beingvaried by the change. of signal strength and the change of decrement is preferably made proportional to the rate of change of signal current in the receiving circuit tuned to the signal wave and comprising the aerial 24 the amplifier 26 and the detector 27 The aerial 25 which is resonant to the spacing waves is connected to a receiver similar to that described with reference to the aerial 24 the elements 16, 26', 27', 28' and 29' of said receiver connected to the aerial 25 is interconnected by the transformer 28' and conductors 28 to the valve 29 which is placed across the aerial 24 by the conductors 29 and 29 so as to control the decrement of the aerial 24. The constant portion of the decrement of the antenna is reduced to a low value by connecting thereto a suitable negative resistance device. In the example shown the decrement of the antenna 24 is reduced by means of the back coupling 30 from the first amplifier vvalve 26 and the decrement of the antenna 25 isreduced by a sim'lar back coupling 30' from the first amplifier valve 26% It will be seen that with this modificatiorh.

the decrease of signal current in one circuit decreases the decrement of the other and vice versa and oscillations are more readily brought up to their correct value for although by the modifications hereinbefore described the 'rateof decrease of oscillations may be made infinite 'therate of increase of oscillations dependsfinally on the energy capacity of the oscillatory circuits. In the present modification (Fig. 7) oscillations which are locally produced in one receiving circuit at the inception of the, signal may be made very strong sincethey are dependent on the rate of damping out of the oscillations in the complem'entary receiver. This method of reception will incidentally? decrease or, eliminate the reception of' atmospherics since for the decrement of the circuits to be increased or decreased as may be required it is necessary that an increase of signal strength in -one receiver occurs concurrently with a decrease in the other and vice versa. When an atmospheric or stray ls'recelved the rise and fall of amplitude of oscillations in both receivers. will occur concurrently. This will prevent the rise of stray signals and quickly damp them out when they are produced.

. When telephonyis transmitted by varying the frequency of v.the transmitted waves and'reception' effected by operating on the slopeof the resonance curves of the receiver then two. receiving devices as in Fig. 7 may be employed the wave length and constant decrement of the .receivers being adjusted so that a decrease in signal strength in one receiver occurs concurrently with an increase 'of signal strength in the other.

Although he invention has been described with reference to the reception of wireless telegraphyland telephony it is obvious that it may be applied to any system of high ire-- I: quency signaling such for example as fwired wireless.

' In the examples given "herein the decrementof the antenna is varied by connecting a Variable resistance to the antenna either by putting a variable resistance across the antenna or by connecting it thereto by means of an inductivelor capacitative coupling. 4 However, the decrement of the antenna may be varied f by varying the :output of thenegative reslstance device connected thereto. Figure 8 Illustrates a characteristic of a typical negative resistance device. In accordance with this invention an order that the aerial may have a variable decrement, the said decre-' ment is to be varied according to the rate of change and amplitude of oscillations. The mean voltage applied across the device would be on the curved portion of the characteristic; for example the mean voltage across the device might be represented by the point 32 on the characteristic curve of Fi 8.- Then resistance of the device is increased and the decrement of the aerial is decreased. If the voltage on the device is decreased then the reverse operation takes place. Therefore the electromotive force controlling .the decrement would be applied to vary the mean' -po- In a three-electrode valve being adjusted so that the representative 1 point is on the curved portion of the'valve characteristic. Or the electromotive force controlling the. decrement may be so applied as to vary the mean anode potential of the device the normal operating parts 'of'the.

valve being suitably adjusted. However,

when these methods are used considerable back lash efiect occurs and hence it isn'eccillation. Further a variable resistance 'conslsting of a three-electrode valve may be placed in the anode circuit of-the valve producing the negative resistance efiect and the -essary' that the antenna should not be set either accidentally or intentlonally into 05- grid potential of this resistance valve varied means of the electromotive force controlling the decrement so'thatthe resistance ofchange of amplitude of the incoming oscillations and hence the output from the reactively coupled valve is correspondingly varied. ,7

What I claim is I '-1. The method of reception in high frequency signaling systems, which comprises receiving the signals in a circuit, detecting the received signals, causing the signals after detection to effect a decrease in the decrement of. the valve-varies in proportion to the rate of said circuit while the detected signals are' increasing in strength, and ,causing the signals-'afterdetection to effect-an increase in the decrement of said circuit while the detected signals are decreasing instrength.

2.'The method of reception in high frequency signaling systems, which comprises receiving the signals in an antenna,detecting the received slgals in a circuit connected'with 75 1f the mean voltage is increased t e negative I quency signaling systems,

- signals are quency signaling systems, which comprises receiving the signals in a circuit, detecting the received signals causing the signals after detection to effect a decrease in the decrementv of s'aid circuit'while the detected signals are increasing in strength, causing the signals after detection to effect an increase in the decrement of said circuit while the detected signals are decreasing in strength, and controlling the changes in the decrement of-said circuit by variations in the strength of the signals after detection.

4. The method of reception in high frequency signaling systems, which comprises receiving the signals in a circuit, detecting the receivedsignals, causing the signals after detection to effect a decrease in the decrement of said circuit while the detected signals are increasing in strength, causing the signals after detectionto effect an increase in the decrement of said circuit while the detected signals are decreasing in strength, and contially proportionally to the rate of change of amplitude of the received oscillations- 5. The method of reception in high frewhich comprises receiving the signals in an antenna, the received signals in a circuit connected with said antenna, causing the signals after detection to effect a decrease in the decrement of said antenna while the detected signals are increasing'in strength, causing the signals after detection to effect an increase in the decrement of said antenna while the detected decreasing in strength, and controlling the changes in the decrement of the antenna by the signals after detection substantially proportionally to the rate of change of amplitude of the received oscillations.

6. A receivin system for high frequency signals, comprising a receiving circu t, means for detecting the received signals, and means controlled by the signals after detection for decreasing the decrement of said circuit while the detected signals increase in strength and for increasing the decrement thereof while the detected signals decrease in strength.

7. A receiving system for high frequency signals, comprising a receiving antenna, a circuit connected with said antenna including means for detecting the received signals, and means responsive to variations in the strength of the signals after detection for decreasing the decrement of the antenna while the detected signals increase in strength and detecting for increasing the decrement thereof while 7 the detected signals decrease in strength.

8. A receiving system for high frequency signals, comprising a receiving circuit, means for detecting the received signals, and means whereby the variations in the strength of the signals after detection are caused to effect decreases and increases in the decrement ,.of

' said circuit substantially proportionally to the rate of increase and decrease respectively in the amplitude of the incoming oscillations.

9. A receiving system for high frequency signals, comprising. a receiving circuit, means for rectifying the incoming oscillations, an inductive winding so relatedto the system that rectifiedhigh frequency oscillations pass through it, 'a variable resistance device connected with said receiving circuit, and means for controlling said variable resistance device in accordance with the voltage variations produced by the rectified oscillations across said inductive winding-so that the decrement of said receiving circuit decreases and 1ncreaseswith the rate of increase and decrease respectively of the received oscillations.

' 10. A receiving system for high frequency. signals, comprisinga receiving circuit, means for rectifying the incoming oscillations, an

inductive winding s0 related to the system that rectified high frequency oscillations pass trolling the changes in the decrement of said circuit by the signals after detection substanwinding operatively connected with said variable resistance device and magnetically coupled with said inductive winding so that said variable resistance device is thereby conioo trolled to decrease and increase the decrement of said circuit proportionally to the rate of increase and decrease'respectively in q the amplitude of the received oscillations.

11. A receiving system for high frequency signals, for detecting the received oscillations, a three electrode valve connected with said circuit.

.for controlling the decrement thereof, and

means operatively connected with said control electrode of said valve and responsive comprising a receiving circuit, means to variations in the strength of the oscillations after detection for effecting decreases and increases in the decrement of the circuit proportional :to the rate of increase and decrease respectively in the amplitude of the received oscillations. 12. A receiving system for high frequency signals, comprising a receiving circuit, a negative resistancedevice for reducing the de-- crement of said circuit to a low value, means for detecting the received oscillations, and means responsive to variations in the strength of the oscillations after detection for controlling the output of said negative resistance device so as to effect decreases and-"increases in the decrement of said circuit substantially proportionally to the rate of increase and decrease respectively in the amplitude of the received oscillations. 13. The method of reception of high fre- 'quency signals transmitted on a. plurality of wave lengths which comprises receiving the l signals in a plurality 'ofcircuits which are vtuned respectively to the Wave lengths employed, detecting the received signals, and causing the received signals after detection to eflect a variation in the decrement of one of said circuits when the strength of the detected signals in another of said circuits varies.

In testimony whereof I have hereunto subscribed my name this eighth day of August,

1923. v ERNEST YEOMr XN ROBINSON. 

